Invasive Bark and Ambrosia Beetles in California Mediterranean Forest Ecosystems

Abstract

This chapter discusses the native ranges, histories of introduction, recent research efforts, and the potential impacts of some of 22 species of invasive scolytids in California’s Mediterranean forest ecosystems. The diversity of native and ornamental tree species, the varied climatic zones, and the widespread importation of nursery stock and packaged cargo have made California a fertile location for the introduction and establishment of bark and ambrosia beetles. Eight of the twenty two taxa are ambrosia beetles; four are spermophagous (e.g., Coccotrypes and Dactylotrypes sp.); six are hardwood bark beetles (Hypothenemus eruditus, Scolytus sp., Phloeotribus liminaris, and Pityophthorus juglandis); and four are coniferophagous bark beetles (Hylurgus ligniperda, Ips calligraphus, Orthotomicus erosus, and Phloeosinus armatus). Five of the species have probable native ranges elsewhere in North America (indigenous exotic species), whereas nearly all of the remaining species have likely origins in Eurasia with at least four of those with clear roots in true Mediterranean ecosystems. Several appear to be from Africa. Many of the species were first detected in heavily urbanized southern California. Detailed overviews are provided for an ensemble of species that have had or could potentially have the most impact on California forest or orchard resources (H. ligniperda, O. erosus, P. juglandis, Scolytus multistriatus, S. rugulosus, S. schevyrewi, and Xyleborinus saxeseni). Another potentially damaging species, the polyphagous shot hole borer, Euwallacea nr. fornicatus, is treated elsewhere (Chap. 26). The introductions of these taxa range from species that may have invaded over 100–150 years ago (e.g., Hypothenemus eruditus, S. rugulosus, or X. saxeseni) to 10–15 years ago (10 of the 22 species have been detected since 2000). Dactylotrypes longicollis (a spermophage); Euwallacea nr. fornicatus; and Hylurgus ligniperda represent new generic records for California. Trends and conditions that favor future invasions by other members of this group of insects and a California watch list are presented.